title: Ectopic expression of miR160 results in auxin hypersensitivity, cytokinin hyposensitivity, and inhibition of symbiotic nodule development in soybean.
abstract: Symbiotic root nodules in leguminous plants result from interaction between the plant and nitrogen-fixing rhizobia bacteria. There are two major types of legume nodules, determinate and indeterminate. Determinate nodules do not have a persistent meristem, while indeterminate nodules have a persistent meristem. Auxin is thought to play a role in the development of both these types of nodules. However, inhibition of rootward auxin transport at the site of nodule initiation is crucial for the development of indeterminate nodules but not determinate nodules. Using the synthetic auxin-responsive DR5 promoter in soybean (Glycine max), we show that there is relatively low auxin activity during determinate nodule initiation and that it is restricted to the nodule periphery subsequently during development. To examine if and what role auxin plays in determinate nodule development, we generated soybean composite plants with altered sensitivity to auxin. We overexpressed microRNA393 to silence the auxin receptor gene family, and these roots were hyposensitive to auxin. These roots nodulated normally, suggesting that only minimal/reduced auxin signaling is required for determinate nodule development. We overexpressed microRNA160 to silence a set of repressor auxin response factor transcription factors, and these roots were hypersensitive to auxin. These roots were not impaired in epidermal responses to rhizobia but had significantly reduced nodule primordium formation, suggesting that auxin hypersensitivity inhibits nodule development. These roots were also hyposensitive to cytokinin and had attenuated expression of key nodulation-associated transcription factors known to be regulated by cytokinin. We propose a regulatory feedback loop involving auxin and cytokinin during nodulation.
authors.affiliation: Department of Plant Science, South Dakota State University, Brookings, South Dakota 57007, USA.
authors.forename: Marie
authors.initials: M
authors.lastname: Turner
authors.forename: Narasimha Rao
authors.initials: NR
authors.lastname: Nizampatnam
authors.forename: Mathieu
authors.initials: M
authors.lastname: Baron
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Coppin
authors.forename: Suresh
authors.initials: S
authors.lastname: Damodaran
authors.forename: Sajag
authors.initials: S
authors.lastname: Adhikari
authors.forename: Shivaram Poigai
authors.initials: SP
authors.lastname: Arunachalam
authors.forename: Oliver
authors.initials: O
authors.lastname: Yu
authors.forename: Senthil
authors.initials: S
authors.lastname: Subramanian
mesh_terms: D001593:Benzyl Compounds; D020369:Bradyrhizobium / Q000502:physiology; D003583:Cytokinins / Q000378:metabolism / Q000494:pharmacology; D018506:Gene Expression Regulation, Plant; D007210:Indoleacetic Acids / Q000378:metabolism* / Q000494:pharmacology; D007701:Kinetin / Q000494:pharmacology; D035683:MicroRNAs / Q000378:metabolism*; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic; D011687:Purines; D053204:Root Nodules, Plant / Q000187:drug effects / Q000502:physiology*; D013025:Glycine max / Q000187:drug effects / Q000502:physiology*; D013559:Symbiosis / Q000502:physiology
chemical_list: D001593:Benzyl Compounds; D003583:Cytokinins; D007210:Indoleacetic Acids; D035683:MicroRNAs; D011687:Purines; C480551:benzylaminopurine; D007701:Kinetin